Method of making a liquid microcell



m 16, 1966 a. A. SAUNDERS 3,266,967

METHOD 0? KING A LIQUID IICROCBLL Original Fahd Jan. 25, 1962 1:! RADIMION INVENTOR scum): RAYMOND A. SAUNDERS BY Z4; M;

ATTORNEY! United States Patent 0 3,266,967 METHOD OF MAKING A LIQUID MICROCELL Raymond A. Saunders, Hyattsville, Md., assignor to the United States of America as represented by the Secretary of the Navy Original application Jan. 25, 1962, Ser. No. 168,852, now Patent No. 3,194,111, dated July 13, 1965. Divided and this application Nov. 29, 1963, Ser. No. 327,154

4 Claims. (Cl. 156-254) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties, thereon or therefor.

This application is a division of application Serial Number 168,852, filed January 25, 1962, for a Variable Space Infrared Liquid Microcell, now Patent No. 3,194,- 111 issuedJuly 13, 1965.

The present invention relates to spectroscopy in general, and more particularly, to spectroscopy of very small samples.

To obtain spectra of very small liquid samples having all absorption bands in the desired transmission range, it has been necessary up to the present time for the spectroscopist to prepare a plurality of separate fixed-thickness cells before proceeding with the spectral analysis.

In processing the separate cells there has been considerable loss of the sample occurring with many filling or emptying operations. The procedure of using cells of fixed-thickness requires also that there be two openings into the sample space, with filling of the sample space accomplished either by capillarity or by forcing or drawing the liquid into the cells through one of the openings by applying pressure or suctiton at the other. The fixed-thickness cells are made by grinding and polis ing suitable alkali-halide crystalline material to produce window surfaces that are reasonably flat, parallel and transparent. Openings must be drilled through or into these windows, and the composite operation is difiicult, expensive, and slow in completion, especially where very small, thin and fragile windows are required for the microcells.

The present invention is directed toward the method of making and using a liquid microcell which avoids the many disadvantages of fixed-thickness cells and provides a microcell of variable space which permits the spectroscopist to obtain spectra of very small liquid samples of the order of 0.1 to 10 microliters at any desired optical pathlength. Only one sampling operation is required with the cell of the present invention. Accordingly, it is an object of the present invention to provide a cell for containing microliquid samples in which many optical pathlengths are provided in a single cell.

It is another object of the present invention to provide a microcell for containing liquid samples which may be filled through one filling operation and with only one opening therein.

It is a further object of the present invention to provide a microcell for liquid samples which may accomodate conveniently samples of the order of 0.1 to 10 microliters.

It is a still further object of the present invention to provide a microcell for the spectroscopic analysis of small liquid samples in which no optical finishing is required in the making of the cells.

It is a still further object of the present invention to provide an inexpensive easy and simple method for making and using a liquid microcell.

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Other objects and many of the attendant advantages of this invention will be readily appreciated as the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 illustrates a preliminary step in forming a liquid microcell according to the present invention.

FIG. 2 illustrates a subsequent step in forming a liquid microcell according to the present invention.

FIG. 3 illustrates a further step in forming a liquid microcell according to the present invention.

FIG. 4 illustrates the final steps in forming and using the liquid microcell of the present invention for spectroscopic analysis of a liquid sample.

The present invention permits a spectroscopist to obtain spectra of very small liquid samples at any desired optical path with but only one cell and a single cellfilling operation. The spectroscopist can select the pathlength or pathlengths to give the optimum spectrum for the purpose desired.

Referring now to FIG. 1 there is shown an alkalihalide crystal 11, such as potassium bromide, which has a dab of an epoxy resin 12 at one end thereof. The crystal is split along the line 13 to form halves 14 and 15 as shown in FIG. 2, and then the two halves are opened slightly as shown in FIG. 3 to provide liquid sample opening 17. The preferred method of splitting the crystal block is by cleaving it along substantially colinear crystalline planes.

The portions 14 and 15 are joined as shown in FIG. 4 by plates 20 and 21 which are sealed to the crystall 11 by a cement which is preferably impervious to the liquids to be examined. When the cement has hardened the cell is ready for use and is filled by touching a micro pipette 18 containing the sample liquid to the open end 23 of the cell. The cell fills instantly by capillary action and is stoppered where necessary by pressing a small tab of silicone rubber putty (uncured elastomer) 24 over open end 23 thereof. Silicone rubber putty or suitable pressure sensitive tape, which in many instances is the more desirable stopper, is used since the putty or tape adhesive is insoluble in most solvents, however, other similar components may be used if the silicone is soluble in a particular liquid being examined. In the majority of spectral analyses the stopper would not be necessary since the liquid would be retained in the cell by capillary action, however, where the volatility of the sample fluid is a factor, a stopper of the type described may be essential.

In practicing the present invention a dob of epoxy resin is placed on one end of a selected alkali-halide crystal blank. The crystal blank is then cleaved along a longitudinal plane substantially bisecting the crystal and the two halves spread slightly at the end opposite the epoxy resin. The space between the two halves of the crystal blank is then transformed into a liquid receiving cavity by securing a pair of side plates, one to each adjacent edge of each crystal half in a liquid tight relationship. The liquid to be analyzed is then introduced into the cavity through the remaining open end by touching a micro-pipette or similar liquid container thereto. The cell is then sealed, when necessary, by closing off said remaining open end with an insoluble cement or putty.

The liquid containing microcell will then provide pathlengths of varying dimension for purposes of spectral analysis which analysis may be accomplished by moving the cell longitudinally, in the manner indicated by arrow 25 in FIG. 4, past a radiation beam emanating from a conventional radiation source 26 such tht a plane through the cell equidistant from the crystalline windows moves perpendicular to the radiation beam. Of course the analysis can alternatively be performed by moving the radiation source parallel to the above described plane while the cell remains stationary.

The invention thus provides a cell which permits a spectroscopist to obtain spectra which exhibit optimum absorption intensity for the sample quantity available and to change pathlength without expending sample fluid whereby pathlengths of greater or lesser absorption intensity may be obtained. For example, with the tapered cell of this invention a spectrum of liquid benzene can be obtained with all absorption bands within the useable transmission range. The cell will perform all desirable and necessary functions of conventional macro variable space cells and in addition can do this for spectral examination of very small samples, of the order of 0.1 to 25 microliters. at optical pathlengths of from zero to one mm. or greater.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. The method of forming a liquid microcell from which a plurality of absorption intensity measurements may be obtained through use of a single cell comprising the steps of cleaving a single crystal of suitable material along a plane substantially bisecting the crystal,

restraining the cleavage from progressing beyond a selected point at one end of said crystal, spreading apart the two sections at the end opposite said one end to form a tapered space which approaches zero thickness at said one end, and

enclosing the space between said spread apart sections on two sides thereof.

2. The method of forming a liquid microcell comprising the steps of adhering a cement to one end of a crystal block, cleaving said crystal block into two sections along a longitudinal plane, spreading said two sections apart at the end remote 5 from said cement, and

enclosing the space between said spread apart sections on two sides thereof by securing a plate to each pair of converging edges of said sections. 3. The method of forming a liquid microcell compris- 30 ing the steps of adhering a dab of epoxy resin to one end of a crystal block, cleaving said crystal block into two sections along a longitudinal plane, spreading said two sections apart at the end remote from said resin to form a tapered space, and securing a plate to each pair of converging edges of said sections. 4. The method of forming a liquid microcell compris- 20 ing the steps of adhering a cement to one end of a block of alkalihalide crystalline material, cleaving said block into two halves along a longitudinal plane thereof, spreading said halves apart at the end remote from said cement to provide a V shaped space, and enclosing said space between said spread apart halves by securing a plate to each pair of diverging edges of said halves to define a fluid retaining cavity of varying cross-sectional area open at its point of greatest cross-sectional area.

References Cited by the Examiner UNITED STATES PATENTS 6/1939 Philipsen 88l4 5/1942 Parker.

10/1954 Coates 88-14 2/1963 Weir et al 88l4 X D. R. STEVENS, T. L. HUDSON, Assistant Examiners. 

1. THE METHOD OF FORMING A LIQUID MICROCELL FROM WHICH A PLURALITY OF ABSORPTION INTENSITY MEASUREMENTS MAY BE OBTAINED THROUGH USE OF A SINGLE CELL COMPRISING THE STEPS OF CLEAVING A SINGLE CRYSTAL OF SUITABLE MATERIAL ALONG A PLANE SUBSTANTIALLY BISECTING THE CRYSTAL, RESTRAINING THE CLEAVAGE FROM PRORESSING BEYOND A SELECTED POINT AT ONE END OF SAID CRYSTAL, SPREADING APART THE TWO SECTIONS AT THE END OPPOSITE SAID ONE END TO FORM A TAPERED SPACE WHICH APPROACHES ZERO THICKNESS AT SAID ONE END, AND ENCLOSING THE SPACE BETWEEN AND SPREAD APART SECTIONS ON TWO SIDES THEREOF. 